The present invention relates to an isolation valve assembly and more particularly to an isolation ball valve assembly for incorporation in pipelines.
The current working practice in the pipework and plant installation industries (onshore and offshore) is, for safety reasons, to fit at predetermined locations within a fluid pipeline an isolation valve assembly in the form of two single ball valve units adjacent to one another. The ball valve units are flange-connected to one another and each is in turn flange connected to a respective adjacent pipeline end. The overall length of each ball valve unit is in accordance with International Standards such as ANSI B16.10, DIN and the like.
The ball valve units are both closed, for example, while workers are working downstream of the isolation valve assembly with the safety of the workers being ensured and maintained should one of the ball valve units fail.
A double ball isolation valve assembly having two ball valves mounted within a common housing is described in our UK Patent No. 2271164. The valve assembly enables two ball valves to be accommodated into a standard length for a single valve assembly. The described assembly is only suitable for use with pipelines having bores of up to and including about 2xe2x80x3 (5.08 cm) since it uses floating balls. Such balls are permitted to float in an axial direction when they are in closed positions so as to prevent adverse loading on an operating stem attached to each ball and to compensate for expansion and contraction as a result of temperature changes. In pipelines having bores of greater that 2xe2x80x3 (5.08 cm) diameter it is generally necessary to use trunnion-mounted ball valves as these are able to withstand the thrust generated by the greater pressures. The ball valves are fixed in position relative to the housing by the trunnions but are free to rotate relative to the valve seats that are spring loaded. Valve seats for trunnion valve balls take up a greater length than simple O-ring or other seats that can be used with floating ball valves. In view of this it has not so far been possible to provide a double ball valve assembly having a standard length for a single ball valve unit for use with the larger pipelines.
It is an object of the present invention to obviate or mitigate the aforesaid problem and to provide for an isolation valve assembly with a double ball valve assembly that is accommodated into the ANSI (or equivalent) length for a single ball valve.
According to the present invention there is provided an isolation valve assembly for use in a pipeline, the assembly comprising a valve housing body having inlet and outlet openings and in which is disposed a pair of independently operable rotary valve balls each having a port therethrough, the balls being rotatable between an open position in which the port is in communication with the adjacent opening and a closed position in which the valve ball closes the adjacent opening, a valve seat supporting each valve ball in the housing and a valve seat retention member disposed in one of the openings and defining a flow passage therethrough for communication with the adjacent valve ball port, the retention member having a first end proximal to one of the valve balls and which supports said valve seat and a second end for engagement with a pipe-fitting of the pipeline.
The provision of a valve seat retaining member that is disposed in the housing body allows the length of the valve assembly to be reduced in comparison to prior art designs such that the length of the assembly conforms to International Standard ANSI B16.10 or equivalent. This means that the assembly (with two valve balls) can be used to replace a valve assembly having a single valve ball in an existing pipeline without the need to modify the pipeline.
Preferably there is provided a valve seat carrier intermediate the retention member and the valve seat. The seat carrier may have a recess into which the valve seat is fitted.
Ideally the valve seat is biased towards the respective valve ball. The biasing force may be provided by a biasing member that is housed in a recess in the valve seat carrier or, alternatively, in a recess in the retention member.
The retention member is preferably substantially wholly received in housing and may be fixed to the housing body by, for example, at least one bolt or by threaded engagement therewith.
The valve balls are preferably each rotatably disposed on at least one trunnion.
There may be provided a recess for a seal in the second end of the retention member.